Theory And Application On Integrated Inductive-filtering Method For Twelve-Pulse Rectifier Transformers

With the prosperity and development of China's national economy,the installed power generation capacity and the total electricity consumption of China increase consistently.According to the 13^th five-year plan for development of China's electric power,it is predicted that in 2020,the installed power generation capacity reaches 2billion kilowatts and the total electricity consumption reaches 6.8⁷.2 trillion kilowatt-hours.In this case,the per capita installed power generation capacity and the per capita total electricity consumption are approaching the level of moderately developed countries in the world.Moreover,the percentage of the electric power in terminal energy consumption will be raised to 27.Consequently,the urge of electric power consumers for high-quality electric power is increasingly enhanced,with the increase of proportion of electric power in terminal energy consumption.With respect to the development strategy in China,the guideline of“Saving,Cleanliness and Safety”as well as the goal of“Cleanliness,High-efficiency,Safety and Sustainability”is confirmed.In practical application of large-power industrial rectifier units,high voltage direct current transmission,low-voltage distribution networks,and so forth,there are generally existing harmonic pollutions and hazards resulting from nonlinear loads such as power electronic devices.In an attempt to explore new techniques of harmonic suppression for 12-pulse rectifier systems,in this dissertation,theory and technique of integrated inductive-filtering for 12-pulse rectifier transformers are proposed,based on the new inductive filtering technique for 12-pulse rectifier transformers as well as a new integrated magnetic method of filtering-inductor integrated with transformer.The major researches performed in this dissertation are as follows.?1?Overview on 12-pulse rectification and integrated magnetic technologies.A general summary of fundamental mechanism and operating characteristics of the12-pulse rectifier systems is provided,detrimental harmonic impacts on rectifier transformers and harmonic suppression methods and their overseas and domestic research status for 12-pulse rectifier systems are described.In addition,an outline of integrated magnetic techniques associated with transformers and inductors is introduced,including the overseas and domestic research status and development.?2?Inductive filtering method for rectifier transformers.Basic introductions on the inductive filtering method,including the development history,operating mechanism,implementation and technical characteristics,are presented.Mechanism of the inductive-filtering rectifier transformers on harmonic current reduction and harmonic magnetic fluxes attenuation in magnetic core are explained in detail,to reveal the essence of inductive filtering.The implementation of zero equivalent impedance of the inductive-filtering windings and the design of fully-tuned harmonic filters are elaborated.Finally,based on practical application examples of inductive-filtering transformers,technical advantages of the inductive filtering method in harmonic current elimination,transformer-core harmonic magnetic-fluxes suppression,power losses reduction and energy saving,inverter commutation failures resisting,and transformer vibration and noise reduction are stated.?3?Proposed harmonic-suppression theory of the new 12-pulse inductive-filtering rectifier system.On the basis of the existing 12-pulse inductive-filtering rectifier transformer technique,a new scheme of parallel filtering windings connection of12-pulse inductive-filtering rectifier transformer unit is proposed for elimination of harmonics in the orders of 5,7,17,19,etc.Moreover,tuned harmonic filters for 11^thh and 13^th harmonic reduction are connected onto parallel links of the filtering windings.Regarding to theoretical analysis,harmonic suppression mechanism of the new12-pulse inductive-filtering rectifier system is presented in accordance with the current expression of Fourier series.With respect to simulations,based on the benchmark model and the general parameters of an actual HVDC project,a PSCAD/EMTDC simulation model of a bipolar HVDC system with dual 12-pulse configuration are built.With this model,scenarios in which the traditional grid-side harmonic filtering scheme and the new inductive-filtering scheme are adopted respectively at the rectifier stations are emulated and compared,attempting to illustrate the outstanding harmonic reduction performance by means of the new 12-pulse inductive-filtering topology.Additionally,a prototype experimental platform is established to verify the harmonic suppression performance of the proposed new 12-pulse inductive-filtering rectifier system.?4?Proposed theory on non-orthogonal decoupling and filtering inductor integration.The non-orthogonal decoupling theory and its implementation are proposed,and the integration design of filtering inductor and transformer is realized,which enables the reduction in total space occupation of the rectifier transformer and harmonic filters.The physical structure of the non-orthogonal decoupling winding constituted by two parallel sub-windings with identical coil turns and inversed twisting directions is described,and the mutual and leakage magnetic fields as well as the decoupling features of this winding are analyzed.In the light of the proposed non-orthogonal decoupling theory,the integration methodology for filtering inductor and transformer is achieved.Moreover,the formula on inductance calculation for integrated filtering inductors is deduced and two methods for decoupling coefficient evaluation of the integrated filtering inductors are shown.The basic structure of filtering-inductor integrated transformer is presented.Theoretically,on the basis of the equivalent circuit model and the circuit equations of coupled inductor,the decoupling characteristic of the integrated filtering inductors is analyzed.Regarding to simulations,take an integrated harmonic filtering distribution transformer as an example,a corresponding Ansys/Maxwell three-dimensional finite-element model is established.And according to the obtained inductance matrix and magnetic coupling coefficient matrix by simulation,the decoupling characteristic of the integrated filtering inductors is analyzed and validated.Moreover,simulations on harmonic suppression of the fore-mentioned distribution transformer are performed.Finally,to verify the correctness of the theoretical analysis and simulation results,a prototype of integrated harmonic filtering distribution transformer is prefabricated and relevant experimental tests are conducted.?5?Proposed theory on the integrated inductive filtering technique for 12-pulse rectifier transformers.Based on the techniques of new 12-pulse inductive filtering and integrated filtering inductors,a new harmonic suppression method,i.e.the integrated inductive filtering technique for 12-pulse rectifier transformers,is further proposed.Relative to theoretical analysis,according to the equivalent impedance circuit of the12-pulse integrated inductive-filtering rectifier system and the Fourier analysis method,the harmonic attenuation mechanism is described.Regarding to simulation analysis,the field-circuit coupling model of the 12-pulse integrated inductive-filtering rectifier system is established by means of Ansys/Maxwell and Ansys/Maxwell Circuit,for simulation verification on harmonic reduction performance of the proposed system.For experimental validation,the prototype of the 12-pulse integrated inductive-filtering rectifier transformers are manufactured,and an experimental platform of the presented 12-pulse integrated inductive-filtering rectifier system is build to verify the outstanding performance on harmonic elimination of the integrated inductive-filtering scheme.In this dissertation,by means of theoretical analysis,simulations,and prototype fabrication and experiments,the theory and application on integrated inductive-filtering for 12-pulse rectifier transformers are performed,the research framework of harmonic suppression theory and application on the proposed 12-pulse integrated inductive-filtering rectifier system is constructed,which are very helpful for promotion and application of the integrated inductive-filtering technique for 12-pulse rectifier transformers.